* Promote ChiselEnum user APIs from experimental (#2929)

They are commonly used and if we were ever to change them, we will need
to go through a deprecation process anyway.

Note that the EnumAnnotations remain in chisel3.experimental because,
like all Chisel annotation support, they are slated to be deprecated and
removed.

(cherry picked from commit 424e9446f1675fe0168e22bdfbbe85db997376e6)

# Conflicts:
#	docs/src/cookbooks/verilog-vs-chisel.md
#	docs/src/explanations/chisel-enum.md

* Maintain binary compatbility, use aliases in chisel3 package

* Deprecate the actual classes in chisel3.experimental
* Also fix backport conflicts

Co-authored-by: Jack Koenig <koenig@sifive.com>

* Check for Vec subaccess in NamedComponent and throw a nicer error. (#2907)

This would previously end up throwing an exception later, when trying
to create a component name and realizing that it was invalid. Instead,
this detects Vec subaccesses early, and gives a more precise error and
suggestion.

(cherry picked from commit d8c30961c7b293ee19024a487698630367ee71c6)

# Conflicts:
#	core/src/main/scala/chisel3/internal/Builder.scala

* Resolve backport conflicts

Co-authored-by: Mike Urbach <mikeurbach@gmail.com>

ChiselEnums check if they should create annotations every time an
instance of them is bound. Because so many annotations would be created,
they check to see if an equivalent annotation has already been added to
the annotations. Previously, this used a linear search of the
annotations, now it uses a HashSet.

(cherry picked from commit 96bde092e449281dc70ebdb05f21695468c3e5fa)

Co-authored-by: Jack Koenig <koenig@sifive.com>